hardware question ... graphic card. [modified]

[Lost User]

I'd look at a much bigger power supply. ATI Radeon HD 6850 1GB requires 131 watts idle and 229 under load. Two of them means 260+ watts idle and 458 or so under load, leaving you with just 200 watts for everything else - something's gotta give. See here[^] Cheers, Drew.

[Maximilien]

I think that will be it. It's a bit weird that Tom's Hardware put in a 650W PSU... maybe it is a new one with bettern pci-e power lead. Thanks.

Watched code never compiles.

[Rutvik Dave]

I agree with Drew. If your PC will not start, no lights/sound at all, then it's PSU. I think your PSU is not 80 Plus so might be you are short just few watts. I had this problem on cheap 585 watt PSU (that came with the case), I bought new blueray and PC will work just fine until I plugin any USB device, it will just shut off the computer. if I remove DVD drive/extra HDD, it will work fine. So if you are planning to buy new PSU, buy at-least 700+ watt 80 Plus Modular PSU (I have this one[^]). And before all this verify that it's the PSU by plugging in just one 6850 (It works with your older card but still). I also build my gaming PC yesterday, but the graphics card (Asus 6970, Now I am thinking to go for GTX 570.) is out of stock since few weeks now, so it's just a nice PC right now. :)

[lewax00]

Maximilien wrote:

Is it possible that my power supply (650w) is not "strong enough"

Yes. 650W is fine for running a single card, but for Crossfire/SLI you're going to need a bit more power. That's exactly the reason I upgraded to a 1000W PSU (you don't need that much unless you're running multiple very high end cards). 750W should be fine I would think.

[Dan Neely]

Rutvik Dave wrote:

If your PC will not start, no lights/sound at all, then it's PSU. I think your PSU is not 80 Plus so might be you are short just few watts.

80+ or not shouldn't have anything to do with it; since any even vaguely reputable PSU is rated by output power not input. If your computer is tripping your circuit breaker a more efficient model might help (and for a computer with a high duty cycle can pay for itself in a year or two), but I wouldn't be entirely comfortable at running wiring at just under peak rated capacity for an extended period (you never know what stupid stuff the last owner might have had hiding in the wall) and would try and move stuff off the circuit on general principles. The other thing I generally advise when sizing a PSU is to overspec it by about 200-300W so that its fan never goes above idle as a noise mitigation strategy. (Yes stock GPU coolers will still be noisy at full load; but two loud fans are worse than just one.)

Did you ever see history portrayed as an old man with a wise brow and pulseless heart, waging all things in the balance of reason? Is not rather the genius of history like an eternal, imploring maiden, full of fire, with a burning heart and flaming soul, humanly warm and humanly beautiful? --Zachris Topelius

[Lost User]

The one on Tom's Hardware probably has more current available on the 12V rails than yours does. Newer PSU's do that because of the demands of newer graphics cards. Cheers, Drew.

[Rutvik Dave]

I was under impression that if the PSU is not 80+, at the full load it will not work efficiently and will lose watts to heat. But I agree with the ~200W buffer.

[Dan Neely]

All PSUs turn their inefficiency percentages into heat; however except for really junky ones that will probably smoke your box before reaching their rated wattage in either current form, all PSUs are rated in terms of DC output not AC input. The difference is that in order to produce 400W of DC a crappy old 70% PSU will consume ~570W of AC, a basic 80% model will consume 500W, a good 85% model 470W, and a top of the line 90% model 445W. The difference between the two values will be radiated as heat. In locations that factor power factor into residential meter rates (EU yes, US no, rest of world ??) the 70% relic will end up costing even more to operate than their base AC consumption would imply since PSUs of that vintage typically had poor to non-existent power factor correction circuitry; in contrast I've never seen an 80+ PSU without at least 95% PFC, 98-99% being typical.

Did you ever see history portrayed as an old man with a wise brow and pulseless heart, waging all things in the balance of reason? Is not rather the genius of history like an eternal, imploring maiden, full of fire, with a burning heart and flaming soul, humanly warm and humanly beautiful? --Zachris Topelius

[Rutvik Dave]

Oh OK, I was subtracting the inefficiency from the max watt... Thanks.

[xympa]

Just because a PSU is 650W doesn't mean that it can't put out more, it just means that the voltages aren't going to be stable, they can always put out at least 50W more if asked, and usually you don't even notice the difference. But it's in those situation that the little details and little faults show, people are running 5870 x2 on Corsairs 650W even thought it's just "tight". My advice would be to either send that PSU back to the manufacturer claiming a fault.

[patbob]

Check how much current of what voltages the graphics card draws. I had to swap my PSU with another of same wattage to get enough 12V amps for my new card (upgrading wasn't an option, unfortunately). There's no standard on how many Amps are available at a given voltage. There's also no guarantee on whether a PSU can actually produce the amps its spec'd to. Like others suggest, a larger wattage PSU, or perhaps just a newer one, might suffice if you don't care to/can't actually figure out what you need.

patbob

[cambiaso]

Max: I recommend you to go to Wikipedia and search for "Power Supply Rail". I believe that very good article will answer most, if not all, of your questions regarding the subject.

[greldak]

Have you got both cards powered using both their required power cables - i.e. a total of 4 power cables to the two carsd? AMD 6800 and 6900 series cards require two power connectors, your 8800gts ony requires one. Also ensure you are not overloading any of the PSU rails - that should cause the PSU to shut down within a few seconds but it doesn't always happen. 650W should be adequate for your setup (although borderline) provided it is a good quality PSU - if it is a generic one replace it.